Next up in America, polygamy?

The movement to legalize multi-partner marriage got a huge boost with this week’s ruling by the U.S. Supreme Court that the federal government must give benefits to same-sex married partners, according to advocates of polygamy.

“We polyamorists are grateful to our brothers and sisters for blazing the marriage equality trail,” Anita Wagner Illig told U.S. News and World Report.

“I would absolutely want to seek multi-partner marriage — it would eliminate a common challenge polyamorists face when two are legally married and others in their group relationships aren’t part of that marriage,” she said.

Illig, head of the group Practical Polyamory, argued it’s a matter of equality – the concept cited by the U.S. court in its decision.

“A favorable outcome for marriage equality is a favorable outcome for multi-partner marriage, because the opposition cannot argue lack of precedent for legalizing marriage for other forms of non-traditional relationships,” she said.

The comments come on the heels of the left-wing of the U.S. Supreme Court deciding that the federal definition of marriage as one man and one woman failed the Constitution’s equality requirement.

“If you change one variable – man and a woman to man and man, woman and woman, you cannot then tell me that you cannot logically … change the other variable, one man, three women. One woman, four men,” he said.

Carey pointed out some British lawmakers are recognizing that if they permit same-sex marriage, there would be no reason to bar two sisters from being married or multiple-partner arrangements.

A California Supreme Court justice, Marvin Baxter, issued a similar warning when his court struck down the state’s ban on same-sex marriage in 2008.

Voters later that year overruled the decision, adopted a state constitutional amendment, Proposition 8, that defined marriage as a relationship between one man and one woman. But a homosexual federal judge, Vaughn Walker, struck down Proposition 8 in 2010.

Baxter dissented from the majority 2008 opinion that created same-sex “marriage” for a short time in the state, arguing the consequences of the decision were not thought out.

He wrote: “The bans on incestuous and polygamous marriages are ancient and deeprooted, and, as the majority suggests, they are supported by strong considerations of social policy. … Our society abhors such relationships, and the notion that our laws could not forever prohibit them seems preposterous.

“Yet here, the majority overturns, in abrupt fashion, an initiative statute confirming the equally deeprooted assumption that marriage is a union of partners of the opposite sex. The majority does so by relying on its own assessment of contemporary community values, and by inserting in our Constitution an expanded definition of the right to marry that contravenes express statutory law.”

His warning?

“Who can say that, in 10, 15 or 20 years, an activist court might not rely on the majority’s analysis to conclude, on the basis of a perceived evolution in community values, that the laws prohibiting polygamous and incestuous marriages were no longer constitutionally justified?”

Carey’s warning was nearly the same.

“Once we let go of the exclusivity of a one-man one-woman relationship with procreation linking the generations, they why stop there?” he said. “If it is about love and commitment, then it is entirely logical to extend marriage to two sisters bringing up children together. If it is merely about love and commitment, then there is nothing illogical about multiple relationships, such as two women and one man.”

Anne Wilde of the polygamy-advocacy organization “Principle Voices,” told Buzzfeed Wednesday, “I think people are more and more understanding that as consenting adults, we should be able to raise a family however we choose.”